Piston ring facings

ABSTRACT

This invention covers piston rings, including compression and oil control rings for internal combustion engine pistons, having a bearing face coated with a hard coating, particularly exhibiting good scuff-resistance comprising either a zirconium oxide base coating or a titanium oxide-aluminum oxide coating. The coating is preferably a plasma jet applied coating formed in situ on the bearing face.

United States Patent Prasse et a1.

[54] PISTON RING FACINGS [72] Inventors: Herbert F. Prasse, Town andCountry; Harold E. McCormick,

Ballwin, both of Mo.

[73] Assignee: Ramsey Corporation, St. Louis, Mo.

[22] Filed: May 11, 1970 [21] Appl. No.: 36,143

[52] US. Cl. ..'.277/235 A, 29/1565 [51] Int. Cl. ..F16j 9/12 [58] Fieldof Search ..1 17/1052, 93.1; 277/216, 223,

[451 Oct. 10,1972

11/1970 Prasse ..277/216 2/1971 Watanabe .....277/224 PrimaryExaminer-Robert 1. Smith Attomey1-Ii1l, Sherman, Meroni, Gross & SimpsonABSTRACT coating, particularly exhibiting good scufi resistancecomprising either a zirconium oxide base coating or a titaniumoxide-aluminum oxide coating. The coating is preferably a plasma jetapplied coating formed in situ on the bearing face.

, it I [56] References Cl ed 4 Claim 6 Drawing Figures UNITED STATESPATENTS is r k 3,310,423 3/1967 Ingram"... 1 17/l05.2

CLLL4///Z/ PISTON RING FACINGS BACKGROUND OF THE INVENTION I. Field ofthe Invention This invention pertains to the piston ring art and to theprovision of bearing faces on piston rings. The inventionv particularlydeals with plasma jet applied coatings and piston rings which exhibitthe desired strength, wear-resistance and scuff-resistance.

2. Description of the Prior Art It is known that piston rings, includingcompression rings and oil control rings, must be coated with a hardfacing metal in order that they demonstrate long-lasting wear.

Suitable piston rings must also demonstrate other desirable propertiesfor passable performance. For example, the coating must have asufficiently high melting point and high particle hardness. In addition,the coating must be porous enough to allow it to carry a lubricant onthe surface of the coating, thus imparting good scuff-resistingproperties. Other properties which should be present include sufficientbond strength between the coating and the basic ring material, and arelatively low coefficient of expansion.

Two of the most important properties are sufficient hardnessto exhibitproper wear and good scuff-resistance so that failure does not occurduring the breakin period. However, while many prior art coatings forpiston rings are sufficiently hard, they do not possess the property ofthe desired degree of scuff-resistance. In many cases, the converse istrue.

It would therefore be of benefit to the art if a new class of pistonring coatings or facings were provided which exhibited all of the aboveproperties, and particularly showed good wear characteristics coupledwith sufficiently high scuff-resistance.

SUMMARY OF THE INVENTION The present invention provides coated pistonrings which show relatively low wear rates, coupled with the desiredhigh degree of scuff-resistance. The rings of this invention have theirbearing face coated with a hard coating exhibiting goodscuff-resistance. The coating comprises either azirconium oxide-basecoating or a titanium oxide-aluminum oxide coating. These coatings aremost preferably applied by means of a plasma jet spraying technique,whereby the coating is formed in situ on the bearing face. If desired,the piston ring bearing face may also contain an underlying bond coatwhich most preferably comprises a nickel-aluminide coating. Suchunderlying coat is particularly useful when the coated rings are used inheavy duty engines.

In accordance with a preferred embodiment of the invention, ferrousmetal compression rings composed of conventionally cast nodular iron ofabout 3-12 percent carbon content by weight, thin rail rings for oilcontrol assemblies composed of carbon steel such as S. A. E. 1070, andthe like base metal rings, are coated with a plasma jet streamcomprising either a powder composed of a combination of aluminum oxideand titanium oxide or a powder composed primarily of zirconium oxide. Apreferred titania-alumina mixture ineludes from about to about percentby weight of titanium oxide and from about 75 to about 90 percent byweight of aluminum oxide.

The plasma jet utilizes a fuel gas preferably composed of a mixture ofnitrogen or argon with or without hydrogen. The compression rings arepreferably peripherally grooved and the groove is filled with an alloyresulting from the plasma jet application of the aluminum oxide-titaniumoxide or zirconium oxide powder. The powder is vaporized and depositedin the ring groove as an in situ formed coating.

It is therefore an object of this invention to provide improved pistonrings with hard-faced bearing surfaces exhibiting good wear andscuff-resistance.

Another object of the invention is to provide piston rings having plasmajet applied alumina-titania or zirconia coatings.

A specific object of the invention is to provide an engine piston ringhaving an annular groove thereon filled with a layer of one of the aboveoxide coatings which have sufficient porosity to allow them to carry alubricant.

Other objects, features and advantages of the invention will be readilyapparent from the following description of certain preferred embodimentsthereof, taken in conjunction with the accompanying drawings, allvariations and modifications may be effected without departing from thespirit and scope of the novel concepts of the disclosure, and in whichthe following detailed description of the annexed sheet of drawings byway of preferred example illustrate several embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG.'1 is a side elevational view,with parts in cross section, of an engine piston and cylinder assembly,wherein the piston has ring grooves equipped with compression and oilcontrol rings each having a bearing face engaging the cylinder which iscomposed of in situ formed plasma jet applied coatings, according tothis invention;

FIG. 2 is an enlarged fragmentary cross sectional view of the topcompression ring in the piston on FIG.

FIG. 3 is a view similar to FIG. 2, but illustrating the secondcompression ring in the piston of FIG. 1;

FIG. 4 is a view similar to FIG. 2, but illustrating the oil controlring in the third ring groove of the piston of FIG. 1;

FIG. 5 is a view similar to FIG. 2, but illustrating the oil controlring in the fourth ring groove of the piston of FIG. 1; and

FIG. 6 is an elevational view of an arbor of piston rings being plasmajet coated in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The piston and cylinderassembly 10 of FIG. 1 illustrates generally a conventional 4-ring grooveinternal combustion engine piston, operating in an engine cylinder. Theassembly 10 includes a piston 11 and an engine cylinder 12 with a bore13, receiving the piston 11. The piston 11 has a head 14 with a ringband 15 having four peripheral ring grooves 16, l7, l8 and 19therearound. The top ring groove 16 has a split solid cast ironcompression or fire piston ring 20 therein. The second ring groove 17has a split solid second compression ring 21 somewhat wider than thering 20. The third ring groove 18 carries a two-piece oil control ringassembly 22. The fourth or bottom ring groove 19 carries a three-pieceoil control ring assembly 23.

As shown in FIG. 2, the top compression or fire ring 20 has a main body24 composed of cast iron, preferably nodular gray iron, with a carboncontent of about 3-1/2 percent by weight. The outer periphery 25 of thisring is covered with a plasmajet applied zirconium oxide or titaniumoxide-aluminum oxide coating 26.

As shown in FIG. 3, the second compression ring 21 has a main body 27composed of the same type of cast iron as the body 24 of the ring 20.The outer periphery 28 of the body 27 is inclined upwardly and inwardlyfrom the bottom edge of the ring, and a peripheral groove 29 is formedaround this inclined periphery. The groove 29 is filled with either ofthe coatings 26.

As shown in FIG. 4, the oil control ring assembly 22 in the third ringgroove 18 is composed of a one-piece flexible channel ring 30 and asheet-metal expander ring 31, having legs extending into the channel forexpanding the ring 30. The ring 30 and the expander are more fullydescribed in the Donald J. Mayhew et al. U.S. Pat. No. 3,281,156.

The one-piece control ring 30 has a pair of axially spaced, radiallyprojecting beads 32. The peripheries of these beads 32 are coated withthe coating 26.

In FIG. 5, the oil control ring assembly 23 includes a resilientspacer-expander ring 33 supporting and expanding split thin rail rings34. The assembly 33 is of the type disclosed in the Melvin W. Marien US.Pat. Nos. 3,133,341 and 3,133,739. The outer peripheries of the railrings 34 are coated with the coating 26, according to this invention.

From the above description, it will be understood that the bearing facesof each of the compression and oil control rings 20, 21, 22 and 23 arecoated with either one or the other coatings described in thisinvention. These bearing faces 26 ride on and sealingly engage the bore13 of the engine cylinder 12, and the rings are compressed in the bore13, so as to expand tightly against the bore wall, and maintain a goodsealing sliding engagement therewith.

As shown in FIG. 6, the coatings 26 are applied on the rings as forexample on the grooved rings 21 by stacking a plurality of the rings onan arbor 35, with the rings compressed so that their split ends will bein near abutment. The arbor clamping the stack of rings in their closed,contracted position may be mounted in a lathe and the peripheries of therings machined to form the grooves 29 therearound. The outer peripheriesof the rings 21 on the arbor are then coated with the coatings 26 from aplasma jet spray gun 36. The gun 36 includes an insulated casing such asNylon 37, from which projects a rear electrode 38, the projection ofwhich is adjustably controlled by a screw knob 39. The front face of thecasing receives a front electrode 40. The casing 37 and electrode 40 arehollow and waterjacketed so that coolant may circulate therethrough froman inlet 41 to an outlet 42. Plasma jet gas is fed through an inlet 43into the chamber provided by the casing 37 and the electrode 40 to flowaround the electrode 38.

The front end of the electrode 40 provides a nozzle outlet 44 for theplasma flame and the ingredients to form the coating 26 are fed to thisnozzle through a powder inlet 45, just in advance of the dischargeoutlet of the nozzle.

A plasma composed of ionized gas is produced by passing the plasma gasfrom the inlet 42 through an electric arc established between theelectrodes 38 and 40. This plasma gas is non-oxidizing and may becomposed of nitrogen and hydrogen with argon, or helium as a carrier.The plasma flame exuding from the nozzle 44 draws the powder therewithby aspiration and subjects the powder ingredients to high temperatures.The jet stream carries the ingredient or ingredients into the bottom ofthe groove 29 of each piston ring and fills the groove.

It is greatly preferred that the zirconium oxide or titaniumoxide-aluminum oxide coatings be plasma jet applied in situ upon thebearing face of the piston ring as just noted. in the usual case theouter coatings are applied by coating the piston rings from a powder fedto a plasma jet stream.

In some instances it may be preferred to first apply a bond coat betweenthe outer coating of zirconium oxide or titania-alumina coating.Preferred bond coats of this type include both molybdenum andnickel-aluminide. However, in any event, the hardness of the layers ofmulti-layer coatings are found to be the same as if each of the coatingshad been applied by themselves. It should therefore beunderstood, ofcourse, that satisfactory bondings with cast iron are obtained directlywith the zirconium oxide or titania-alumina coatings without the use ofa separate bond-coating material.

A typical underlying coating of nickel and aluminum includes 80-95percent by weight of nickel, with the remainder being aluminum.

The coatings of the invention are applied via a plasma jet spraytechnique either by utilizing a zirconium oxide powder or a combinationof titanium and aluminum oxides. Typically, a titania-alumina coatingwill comprise a 10-25 percent by weight of titanium oxide and -90percent aluminum oxide. A specific coating will be comprised of 83percent aluminum oxide and 17 percent titanium oxide.

The coatings here have excellent hardness. For example, the hardness ofthe zirconium oxide outer coating is a Vickers Hardness (DPH of at least1,000 and more often ranges between about 1,300 and 1,600. In likemanner, the hardness of the combined coating of titania and alumina isalso quite adequate. The titania phase generally has a Vickers Hardness(DPHM of 500-1500 in this phase. More often the hardness is 800-1 ,200.The alumina phase has a Vickers Hardness (DPH )o of 2,3003,300 and moreoften falls within the range of about 2,500 and 3,000.

It should be noted here that both the zirconium oxide coating and thetitanium oxide-aluminum oxide coating have excellent hardness andscuff-resistance as will be demonstrated hereinafter. Also, saidcoatings may be ground utilizing conventional techniques.

The following examples illustrate typical conditions utilized inspraying the coatings of the invention upon piston rings. In eachinstance, a plasma jet spray technique was utilized.

EXAMPLE I Here a powder was sprayed upon an arbor of rings to produce ahard-faced coating. The specific coating in this example was comprisedof 77 percent alumina and 13 percent titania with the aluminum andtitanium being plasma jet sprayed as a powder mixture of oxides.

The following plasma application parameters were utilized in this run:

Number of Guns Gun-To-Work-distance Angle of Gun to Axis of Work 4%"Compression Rings-45 Oil Rings-90 straight in.

Amperage D.C. 500

Voltage 85 reference Secondary Gas-Hydrogen 15 Std. cubic ft.lhourPrimary Gas 75 Std. cubic ft.lhour Carrier Gas 37 Std. cubic ftJhourRate of Vertical Feed 24-32 inches/minute Speed of Arbor Rotation 60-90RPM based on 4" arbor The spray is applied as shown in FIG. 6 until therings are covered with the titanium oxide-aluminum coating.

' EXAMPLE II A zirconium oxide coating was plasma jet applied here byfollowing the below variables with respect to the plasma jet technique.

arbor diameter.

It has also been noted that the particle distribution size of thezirconium oxide powder utilized in the plasma jet spray technique isimportant particularly to achieve proper tensile strength. If the powderis too coarse the resultant coating has reduced strength and is notporous enough to retain oil. In some :respects, the same is true withrespect to the alumina-titania coating, although particle distributionwith respect to this mixed coating is not as critical.

Forbest results, the zirconium oxide powder should have a particledistribution size of at least 50 percent by weight of less than 40microns. Preferably at least 70 percent of the zirconium oxide powdershould have a particle distribution size less than about 40 microns. Forgood abrasive wear-resistance, the alumina-titania powder will rangefrom about 270 mesh up to about +15 microns.

A typically useful zirconia powder has the following sieve analysis:

25 20 microns -20+ 15 microns -15 10 microns l0 microns In the followinggroup of studies the zirconia and titania-alumina coatings were analyzedafter application to piston rings with respect to grindingcharacteristics, hardness, oxidation resistance and engine test toobtain wear data.

EXAMPLE III In this first series of tests, a piston ring was coated witha hard outer zirconia coating and underlying molybdenum coating. Anotherseries of pistons were coated with an outer coating of 77 percentalumina and 13 percent titania. Both series of coatings could be groundusing normal grinding practices.

EXAMPLE IV The coatings of Example III were then tested for hardness.With respect to the zirconia-molybdenum coating the outer zirconiacoating had a hardness of 1,592 Vickers (DPI-I) and the underlyingmolybdenum coating had a hardness of 922. The coating comprising a blendof aluminum oxide and titanium oxide had a Vickers Hardness (DP'I-I). of2,778.

EXAMPLE V The coatings of Example III were then subjected to extensiveheat treatment in order to indicate the degree of oxidation as measuredby major color changes. Both coatings, when heated at 750 F. for 100hours did not indicate any oxidation. In fact, the coating comprisingaluminum oxide-titanium oxide did not indicate oxidation even whenheated at l,000 F. for 100 hours.

With respect to the above coatings, no significant hardness changes wereobserved on any of the coatings before and after heating to either 750F. or 1,000 F. for the 100 hour period.

EXAMPLE v1 Still further testing was carried out with respect to pistonrings having either a zirconium oxide coating or a blend of aluminumoxide and titanium oxide as a coating. In a porosity test, the zirconiumoxide coating had a porosity of 10-15 percent and the blended coating aporosity of about 3 percent. The zirconium oxide coating had a meltingtemperature of 4,650 F. and the blend of aluminum oxide-titanium oxidecoating had a melting temperature of about 3,500 F.

EXAMPLE VII Both the zirconium oxide and alumina-titania coatings onpiston rings were also subjected to engine tests in a Renault mm testengine in order to determine wear characteristics. Both coatings werefound to be acceptable and in many cases superior to conventional pistonring coatings.

Specifically, both end clearance change and bore wear data wereobtained. With respect to the end clearance change the followingprocedure was carried out. The rings were first confined in a precisediameter gauge. In order to avoid a change in end clearance (E.C.) dueto small changes in gauge diameter, the

same gauge was used before and after the test. The end clearance betweenthe two gap ends was then measured using a tool makers microscope with acalibrated lens system. Thereafter, the rings were installed and theengine run in a specific test schedule for the prescribed length oftime. After the test was completed the rings were removed from theengine, any carbon accumulation carefully removed, and the abovemeasurement repeated. The difference between the two measurements in endclearance then is a measurement of wear.

With respect to the bore wear test, each bore was measured before thetest at five locations in two directions at each location. Measurementswere taken of the cylinder both lengthwise and across at the fivecations from the top of the cylinder bore as follows:

1. At top of ring travel approximately threeeighths inch 2. One inchfrom top 3. Two inches from top 4. Three inches from top 5. Four inchesfrom top.

This procedure was then repeated after the test and the difference wascalculated for each position.

Both coatings from a ring wear standpoint and a bore wear standpointpassed the above test, and in many instances were superior toconventional piston ring coatings with respect to wear characteristics.Data are given in Tables 11 and 111.

TABLE II Zirconium Oxide Coating Cylinder no. l 2 3 4 top ring before.023 .022 .023 .024 after .024 .023 .024 .025 average change .001 .001.001 .001 2nd ring before .024 .024 .023 .024 after .027 .026 .024 .027average change .003 .002 .001 .003

Bore Wear Test Cylinder no. I 2 3 4 distance from top of cylindercrosswise 3/8 2.7562 2.7563 2.7564 2.7558 before 1 2.7562 2.7563 2.75632.7560 2 2.7563 2.7563 2.7564 2.7564 3 2.7565 2.7566 2.7566 2.7567 42.7565 2.7566 2.7568 2.7567 average 2.7564 2.7564 2.7565 2.7563crosswise 3/8 2.7595 2.7595 2.7582 2.7591 after 1 2.7564 2.7563 2.75622.7562 2 2.7562 2.7560 2.7561 2.7563 3 2.7562 2.7560 2.7562 2.7563 42.7557 2.7558 2.7560 2.7560 average 2.7568 2.7567 2.7565 2.7568 averagechange .0005 .0003 .0000 .0005 lengthwise 3/8 2.7567 2.7570 2.75702.7562 before 1 2.7565 2.7568 2.7568 2.7564 2 2.7565 2.7566 2.75672.7565 3 2.7565 2.7566 2.7566 2.7567 4 2.7560 2.7564 2.7565 2.7564average 2.7564 2.7567 2.7567 2.7565 lengthwise 3/8 2.7586 2.7583 2.75842.7584 after I 2.7558 2.7568 2.7560 2.7554 2 2.7557 2.7563 2.7562 2.75583 2.7559 2.7564 2.7564 2.7562 4 2.7562 2.7563 2.7562 2.7562 average2.7564 2.7568 2.7566 2.7564 average change .0000 .0001 .0001 -.0001

.15 TABLE 111 Aluminum Oxide-Titanium Oxide Coating Distance From Cyl.Cyl. Cyl. Cyl. top of No. 1 No.2 No.3 No. 4 cylinder lengthwise 3/82.7559 2.7557 2.7570 2.7582 before 1 2.7560 2.7560 2.7563 2.7576 22.7564 2.7567 2.7561 2.7565 3 2.7564 2.7569 2.7552 2.7560 4 2.75642.7561 2.7549 2.7559 ave. 2.7561 2.7561 2.7558 2.7567 lengthwise 3182.7563 2.7560 2.7564 2.7583 after 1 2.7556 2.7554 2.7561 2.7573 2 2.75602.7562 2.7556 2.7565 3 2.7561 2.7566 2.7550 2.7558 4 2.7551 2.75652.7549 2.7551 ave. 2.7558 2.7561 2.7556 2.7570 ave. change .0003 .0000.0002 .0003 top ring E. C. before .0236 .0222 .0211 .0224 E. C. after.0255 .0241 .0238 .0257 E. C. change .0019 .0019 .0027 .0033 2nd ring E.C. before .0240 .0244 .0240 .0243 E. C. after .0254 .0263 .0254 .0265 E.C. change .0014 .0019 .0014 .0022 distance from top of cylindercrosswise 3/8 2.7568 2.7571 2.7560 2.7562 before 1 2.7568 2.7572 2.75642.7567 2 2.7563 2.7570 2.7571 2.7573 3 2.7560 2.7565 2.7572 2.7570 42.7564 2.7560 2.7562 2.7570 ave. 2.7565 2.7568 2.7566 2.7569 crosswise3/8 2.7572 2.7571 2.7557 2.7570 after 1 2.7565 2.7571 2.7560 2.7568 22.7560 2.7568 2.7567 2.7566 3 2.7555 2.7580 2.7570 2.7566 4 2.75562.7551 2.7563 2.7560 ave. 2.7566 2.7564 2.7565 2.7561 ave. change .0001.0004 .0001 .0008

SUMMARY The present invention provides hard-faced piston rings havingcoatings of the zirconium oxide or alumina-titania type. The rings ofthe invention are preferably coated utilizing a plasma jet techniquewherein said coatings are formed in situ on the ring. In addition toexcellent hardness the coatings also exhibit superior scuff-resistance.Also, they can be finished by grinding on conventional silicon carbideand aluminum oxide grinding wheels.

We claim as our invention:

1. A piston ring having a bearing face coating of a hard scuff resistingmaterial consisting essentially of a mixture of from about 10 to fromabout 25 percent by weight titanium oxide and from about to aboutpercent by weight aluminum oxide, the titanium oxide being in a firstphase and having a hardness of from about 500 to about 1,500 VickersHardness (DH-1),, the aluminum oxide being in a second phase and havinga hardness of from about 2,300 to about 3,300 Vickers Hardness (DH-1) 2.The piston ring of claim 1 further characterized in that the mixture is17 percent by weight titanium oxide and 83 percent by weight aluminumoxide.

3. The piston ring of claim 1 further characterized in that there is abond coat underlying the hard scuff resisting material, comprisingnickel-aluminide.

4. The piston ring of claim 3 further characterized in that the bondcoat comprises 80 to percent by weight nickel with the remainderaluminum.

2. The piston ring of cLaim 1 further characterized in that the mixtureis 17 percent by weight titanium oxide and 83 percent by weight aluminumoxide.
 3. The piston ring of claim 1 further characterized in that thereis a bond coat underlying the hard scuff resisting material, comprisingnickel-aluminide.
 4. The piston ring of claim 3 further characterized inthat the bond coat comprises 80 to 95 percent by weight nickel with theremainder aluminum.